Association of Night Snacking and Screen Time on Sleep Behavior in Japanese Toddlers: A Cross-Sectional Study.

BACKGROUND/OBJECTIVES: Irregular lifestyles, such as sleep deprivation and disordered eating, disrupt the circadian clock and are linked to health issues. This study investigates the relationship among chronotypes, social jet lag, night-snacking habits, and screen time in toddlers. METHODS: A survey of 6177 mothers of children aged 3-8 years was conducted in June 2022. Means comparison and multiple regression analyses were used to analyze the data. RESULTS: Toddlers who consumed night snacks were more likely to be evening types and experienced longer social jet lag. Longer screen time during night snacking correlated with evening-type tendencies. Juice and ice cream were identified as evening-type snacks. CONCLUSIONS: We suggest that stopping snacks after dinner is crucial to prevent evening-type eating. Especially, high-sugar and high-fat night snacks like juice and ice cream may contribute to nocturnal habits and disrupt circadian rhythms in children.

Improvement of Jet Lag and Travel Fatigue Symptoms and Their Association with Prior International Travel Experience in Junior Athletes.

Jet lag and travel fatigue can occur after crossing multiple time zones in a short period of time, possibly affecting various aspects of an athlete's behavior. However, there are few studies regarding this issue, particularly considering junior athletes. This study aimed to investigate and quantify the symptoms of jet lag and travel fatigue and the factors impacting these conditions. A survey was completed by 41 Japanese junior athletes (21 men and 20 women), competing at an international game in Finland, to assess their performance, sleeping habits, digestion, fatigue, and jet lag on the first day of arrival and on the opening day of the competition. Although athletes awoke less often during sleep on the opening day of the competition compared with the first day, sleep time, ease of falling asleep, and sleep quality decreased significantly. Prior experience traveling abroad for international competitions was positively associated with improvements regarding ease of falling asleep (coefficient = 2.22, p = 0.01), quality of sleep (coefficient = 2.16, p = 0.02), and alertness after waking up (coefficient = 1.85, p = 0.05) by the opening day of the competition when compared with the results for athletes who had no such prior experiences. Junior athletes experience symptoms of jet lag and travel fatigue that may persist until the day of competition, and prior experience traveling abroad may help in alleviating their symptoms.

Association of sleep and generalized anxiety disorder in Korean adolescents.

BACKGROUND: Generalized anxiety disorder (GAD) is a common anxiety disorder among adolescents, significantly impacting their concentration and learning capabilities. The connection between emotional well-being and sleep is well-established, and Korean adolescents are particularly prone to inadequate sleep. This study aimed to determine the association between sleep duration and GAD in Korean adolescents. METHODS: This study was conducted using data from 106,513 adolescents aged 12-18 years. Data from the 2020-2022 Korea Youth Risk Behavior Survey were used. Sleep duration was classified into five groups, based on an average sleep duration of 7-7.9 h in adolescents. Social jet lag was defined as a misalignment between an individual's biological and social clocks. Differences in sleep duration between weekdays and weekends, social jet lag, and bedtime were each classified into three categories. Multiple logistic regression analysis was performed to evaluate the association between sleep duration and GAD. RESULTS: Comparing the five groups classified based on sleep duration, adolescents in the groups that slept less experienced a significant increase in the odds of developing GAD (adjusted odds ratio [aOR]: boys: 1.10 in the 6.0-6.9-h group, 1.14 in the 5.0-5.9-h group, and 1.23 in the ≤ 4.9-h group; girls: 1.05 in the 6.0-6.9-h group, 1.19 in the 5.0-5.9-h group, 1.22 in the ≤ 4.9-h group). Adolescents with poor sleep quality experienced more frequent instances of inadequate sleep (aOR: boys: 2.51; girls: 2.43). CONCLUSIONS: GAD is strongly associated with insufficient sleep. Consequently, it is imperative to assess and address GAD in adolescents with irregular sleep patterns.

Is Travel Associated With Match Performance in Elite North American Professional Soccer? An Exploratory Study.

PURPOSE: Travel fatigue impacts cognitive and physiologic systems, but its association with elite soccer match performance is unclear. In this retrospective observational study, we aimed to explore the association between travel and match outcomes in elite North American soccer. METHODS: Travel data and match outcomes (team points or goals scored and conceded) and physical performance outcomes from 26 elite professional soccer teams and their players were analyzed (148 matches [team-based data] and 1252 player matches from 297 players; age 22.7 [4.5] y). Player- and match-level correlations between performance measures and both acute and cumulated travel metrics were analyzed. RESULTS: Cumulative travel metrics were positively associated with team (travel distance [r = .20; 95% CI, .03-.25], travel time [r = .20; .06-.37], and time away [r = .20; .06-.37]) and individual player (travel distance, [r = .14; .08-.19], travel time [r = .17-.23], and time away [r = .13; .07-.18]) high-intensity running. Cumulative time away was negatively associated with team points (r = -.14; -.28 to -.001) and positively associated with goals conceded (r = .14; .01-.27); no clear association between acute travel metrics and match outcomes or physical performance was observed. CONCLUSIONS: As travel cumulated, away teams and their players ran more but for less reward (team points), although the magnitude of these associations was small. These data are exploratory and do not imply a causal relationship; however, further research should consider cumulation of travel.

Toward an Indoor Lighting Solution for Social Jet Lag.

There is growing interest in developing artificial lighting that stimulates intrinsically photosensitive retinal ganglion cells (ipRGCs) to entrain circadian rhythms to improve mood, sleep, and health. Efforts have focused on stimulating the intrinsic photopigment, melanopsin; however, specialized color vision circuits have been elucidated in the primate retina that transmit blue-yellow cone-opponent signals to ipRGCs. We designed a light that stimulates color-opponent inputs to ipRGCs by temporally alternating short- and long-wavelength components that strongly modulate short-wavelength sensitive (S) cones. Two-hour exposure to this S-cone modulating light produced an average circadian phase advance of 1 h and 20 min in 6 subjects (mean age = 30 years) compared to no phase advance for the subjects after exposure to a 500 lux white light equated for melanopsin effectiveness. These results are promising for developing artificial lighting that is highly effective in controlling circadian rhythms by invisibly modulating cone-opponent circuits.

Investigation of the effect of circadian rhythm on the performances of NBA teams.

Professional athletes competing in the NBA are frequently exposed to time-zone-shifting travels. These time zone changes may cause circadian rhythm (CR) phase shifts and these shifts affect sportive performance. The aim of this study was to investigate the effects of CR phase shifts on the performance of NBA teams. 25016 regular season games across 21 consecutive seasons were included in the CR phase shift calculations. To examine the CR phase shift effect on team performance, teams were divided into three groups regarding Coordinated Universal Time (UTC): the same internal UTC as the local UTC (LS); the internal UTC ahead of the local UTC (LA); and the internal UTC behind the local UTC (LB). With a different approach, teams were divided into another three categories: the same internal UTC as its opponent's internal UTC (OS); the internal UTC ahead of its opponent's internal UTC (OA); and the internal UTC behind its opponent's internal UTC (OB). 24985 game data were used to compare these groups in terms of 25 variables. Statistical analyses were conducted separately for home and away teams. For home games, it was found that LA and OA are the most and LB is the least successful group in winning and scoring performances. For away games, it was determined that LS is the most advantageous group with the best winning percentage. These results revealed that teams from more west may have a CR advantage in regular season home games. However, it is thought that the performance of away teams depends more on travel fatigue than CR phase shifts.

Associations between temporal eating patterns and body composition in young adults: a cross-sectional study.

PURPOSE: The aim of this study was to examine the associations between body composition and temporal eating patterns, including time of first eating occasion, time of last eating occasion, eating window, and eating jet lag (the variability in meal timing between weekdays and weekends). METHODS: A total of 131 participants were included in the study. Temporal eating pattern information was collected through consecutive 7-day eat timing questionnaires and photographic food records. Body composition was assessed by bioelectrical impedance analysis. Multiple linear regression models were used to evaluate the relationships of temporal eating patterns with body composition, and age was adjusted. Eating midpoint was additionally adjusted in the analysis of eating window. RESULTS: On weekdays, both later first eating occasion and last eating occasion were associated with lower lean mass, and longer eating window was associated with lower body fat percentage. On weekends, both later first eating occasion and last eating occasion were associated with lower lean mass, and longer eating window was associated with higher FFMI. Longer first eating occasion jet lag was associated with lower lean mass. CONCLUSION: Our study suggested that earlier and more regular eating patterns may have a benefit on body composition.

Associations between multiple sleep dimensions and suicide and non-suicidal self-injury: a cross-sectional study of 3828 Chinese young people.

PURPOSE: Suicide and non-suicidal self-injury (NSSI) are preventable concerns in young people. Suicidal ideation (SI), suicidal plans (SP) and suicidal attempt (SA) are closely related to death. Sleep problems are known risk factors for suicide and NSSI. This study aimed to explore the relationship between sleep, suicidality and NSSI. METHODS: Participants were 3,828 middle school and college students aged 11-23 years from urban and rural areas of Henan Province. Sleep, suicidal phenomena and NSSI were assessed by applying self-reported questionnaires. Chi-squared tests were utilized to demonstrate the demographic data and sleep variables. The correlation between sleep, suicidality and NSSI were explored by using binary logistic regression, while adjusting socio-demographic characteristics with multivariate models. RESULTS: Sleep variables except mid-sleep time were related to suicidal phenomena (P < 0.05). Greater social jet lag (SJL) [≥ 2 h (h)] was associated with increased risk of SI [Odds ratios (OR) = 1.72, 95% confidence intervals (CI):1.40-2.11], SP (OR = 2.10, 95%CI:1.59-2.79) and SA (OR = 1.50, 95%CI:1.00-2.26). Non-only child participants with SJL (≥ 2 h) had significantly increased odds of SI (OR = 1.75, 95%CI: 1.41-2.18) and SP (OR = 2.25, 95%CI: 1.66-3.05). Eveningness chronotype had the strongest correlation with SI (OR = 3.87, 95%CI:2.78-5.38), SP (OR = 4.72, 95%CI:2.97-7.50), SA (OR = 6.69, 95%CI:3.08-14.52) and NSSI (OR = 1.39, 95%CI:1.02-1.90). CONCLUSION: Overlong or short sleep duration, SJL, eveningness chronotype and other sleep abnormalities (e.g., daytime dysfunction, low sleep efficiency) were associated with a higher prevalence of SI, SP and SA. Additionally, eveningness was significantly correlated with NSSI among young people. These findings suggested the importance of assessing and intervening in sleep habits to prevent suicide and NSSI in young people.

The Relationship Between Sleep Quality, Sleep Duration, Social Jet Lag and Obesity in Adolescents.

Objective: The frequency of obesity and poor sleep quality among adolescents is increasing and causes many chronic problems. The objective was to investigate the correlation between body mass index (BMI), sleep quality, sleep duration and social jet lag (SJL) among adolescents. Methods: This study is cross-sectional. A cohort of 416 adolescents, ranging in age from 12 to 18 participated in the study. Adolescents were divided into three groups according to BMI SDS: adolescents with normal weight, adolescents with overweight and adolescents with obesity. The Pittsburgh Sleep Quality Index (PSQI) questionnaire was used to determine the sleep quality of the adolescents. The calculation of SJL and sleep-corrected social jet lag (SJLsc) was performed. Results: The mean age of the adolescents was 15.0 ± 2.9 years.There were 222 males (53.4%). SJL and PSQI scores were significantly higher in the adolescents with obesity compared to the adolescents with normal weight and overweight (p < 0.001). An analysis of the relationship between the PSQI and BMI SDS revealed a correlation that was statistically significant (r = 0.667; p < 0.001). Conclusion: Adolescents with obesity reveal poorer sleep quality and a longer duration of SJL compared to adolescents with normal-weight. Moreover, increased SJL was linked to an increase in BMI. Maintaining good sleep quality and less exposure to SJL may help reduce the risk of obesity.

Arginine vasopressin: Critical regulator of circadian homeostasis.

Circadian rhythms optimally regulate numerous physiological processes in an organism and synchronize them with the external environment. The suprachiasmatic nucleus (SCN), the center of the circadian clock in mammals, is composed of multiple cell types that form a network that provides the basis for the remarkable stability of the circadian clock. Among the neuropeptides expressed in the SCN, arginine vasopressin (AVP) has attracted much attention because of its deep involvement in the function of circadian rhythms, as elucidated in particular by studies using genetically engineered mice. This review briefly summarizes the current knowledge on the peptidergic distribution and topographic neuronal organization in the SCN, the molecular mechanisms of the clock genes, and the relationship between the SCN and peripheral clocks. With respect to the physiological roles of AVP and AVP-expressing neurons, in addition to a sex-dependent action of AVP in the SCN, studies using AVP receptor knockout mice and mice genetically manipulated to alter the clock properties of AVP neurons are summarized here, highlighting its importance in maintaining circadian homeostasis and its potential as a target for therapeutic interventions.

Social jet lag impairs exercise volume and attenuates physiological and metabolic adaptations to voluntary exercise training.

Social jet lag (SJL) is a misalignment between sleep and wake times on workdays and free days. SJL leads to chronic circadian rhythm disruption and may affect nearly 70% of the general population, leading to increased risk for cardiometabolic diseases. This study investigated the effects of SJL on metabolic health, exercise performance, and exercise-induced skeletal muscle adaptations in mice. Ten-week-old C57BL/6J mice (n = 40) were allocated to four groups: control sedentary (CON-SED), control exercise (CON-EX), social jet lag sedentary (SJL-SED), and social jet lag exercise (SJL-EX). CON mice were housed under a 12:12-h light-dark cycle. SJL was simulated by implementing a 4-h phase delay for 3 days to simulate "weekends," followed by a 4-h phase advance back to "weekdays," for 6 wk. EX mice had free access to a running wheel. Graded exercise tests (GXTs) and glucose tolerance tests (GTTs) were performed at baseline and after intervention to monitor the effects of exercise and social jet lag on cardiorespiratory and metabolic health, respectively. SJL led to alterations in activity and running patterns and clock gene expression in skeletal muscle and decreased average running distance (P < 0.05). SJL-SED mice gained significantly more weight compared with CON-SED and SJL-EX mice (P < 0.01). SJL impaired fasting blood glucose and glucose tolerance compared with CON mice (P < 0.05), which was partially restored by exercise in SJL-EX mice. SJL also blunted improvements in exercise performance and mitochondrial content in the quadriceps. These data suggest that SJL blunted some cardiometabolic adaptations to exercise and that proper circadian hygiene is necessary for maintaining health and performance.NEW & NOTEWORTHY In mice, disrupting circadian rhythms with social jet lag for 6 wk caused significant weight gain, higher fasting blood glucose, and impaired glucose tolerance compared with control. Voluntary exercise in mice experiencing social jet lag prevented weight gain, though the mice still experienced increased fasting blood glucose and impaired exercise performance compared with trained mice not experiencing social jet lag. Social jet lag seems to be a potent circadian rhythm disruptor that impacts exercise-induced training adaptations.

Efetividade da suplementação de melatonina segundo as revisões sistemáticas Cochrane / Effectiveness of melatonin supplementation according to Cochrane systematic reviews

Contextualização: A melatonina é um hormônio endógeno encontrado em quase todos os organismos e participa de vários processos fisiológicos. A suplementação de melatonina tem sido preconizada na mídia para o tratamento e prevenção de várias doenças. Entretanto, há carência de informações científicas disponíveis sobre seu real benefício para a saúde. Objetivos: Sumarizar as evidências de revisões sistemáticas da Cochrane, referentes à efetividade das intervenções com suplementação de melatonina em humanos. Métodos: Trata-se de overview de revisões sistemáticas Cochrane. Procedeu-se à busca na Cochrane Library (2023), sendo utilizado o descritor "MELATONIN". Todas as revisões sistemáticas de ensaios clínicos foram incluídas. O desfecho primário de análise foi a melhora clínica, a redução dos sintomas ou a prevenção da doença. Resultados: Oito estudos foram incluídos, totalizando 53 ensaios clínicos e 4.024 participantes. Houve evidência de efetividade apenas para controle de ansiedade em pacientes em pré-operatório (evidência moderada) em comparação com placebo e para prevenção e tratamento de jet lag de fuso horário (evidência alta de certeza). Discussão: Embora seja muito veiculada na mídia, a suplementação de melatonina carece de estudos de qualidade para análise de sua efetividade. Os estudos clínicos disponíveis até o momento são heterogêneos e apresentam limitações metodológicas. Poucas análises convergem com segurança para um bom nível de evidência que permita sua recomendação. Conclusão: Não há suporte com bom nível de evidência atualmente para a maioria das intervenções com suplementação de melatonina, sendo recomendada a realização de novos estudos prospectivos para melhor robustez dos achados e análises.

Simulated Chronic Jet Lag Affects the Structural and Functional Complexity of Hippocampal Neurons in Mice.

There has been a long history that chronic circadian disruption such as jet lag or shift work negatively affects brain and body physiology. Studies have shown that circadian misalignment act as a risk factor for developing anxiety and mood-related depression-like behavior. Till date, most studies focused on simulating jet lag in model animals under laboratory conditions by repeated phase advances or phase delay only, while the real-life conditions may differ. In the present study, adult male mice were subjected to simulated chronic jet lag (CJL) by alternately advancing and delaying the ambient light-dark (LD) cycle by 9 h every 2 days, thereby covering a total of 24 days. The effect of CJL was then examined for a range of stress and depression-related behavioral and physiological responses. The results showed that mice exposed to CJL exhibited depression-like behavior, such as anhedonia. In the open field and elevated plus maze test, CJL-exposed mice showed increased anxiety behavior compared to LD control. In addition, CJL-exposed mice showed an increased level of serum corticosterone and proinflammatory cytokine, TNF-α in both serum and hippocampus. Moreover, CJL-exposed mice exhibited a reduction in structural complexity of hippocampal CA1 neurons along with decreased expression of neurotrophic growth factors, BDNF and NGF in the hippocampus compared to LD control. Taken together, our findings suggest that simulated chronic jet lag adversely affects structural and functional complexity in hippocampal neurons along with interrelated endocrine and inflammatory responses, ultimately leading to stress, anxiety, and depression-like behavior in mice.

Addressing Circadian Disruptions in Visually Impaired Paralympic Athletes.

PURPOSE: Transmeridian travel is common for elite athletes participating in competitions and training. However, this travel can lead to circadian misalignment wherein the internal biological clock becomes desynchronized with the light-dark cycle of the new environment, resulting in performance decrement and potential negative health consequences. Existing literature extensively discusses recommendations for managing jet lag, predominantly emphasizing light-based interventions to synchronize the internal clock with the anticipated time at the destination. Nevertheless, visually impaired (VI) athletes may lack photoreceptiveness, diminishing or nullifying the effectiveness of this therapy. Consequently, this invited commentary explores alternative strategies for addressing jet lag in VI athletes. CONCLUSIONS: VI athletes with light perception but reduced visual acuity or visual fields may still benefit from light interventions in managing jet lag. However, VI athletes lacking a conscious perception of light should rely on gradual shifts in behavioral factors, such as meal timing and exercise, to facilitate the entrainment of circadian rhythms to the destination time. Furthermore, interventions like melatonin supplementation may prove useful during and after travel. In addition, it is recommended that athlete guides adopt phase-forward or phase-back approaches to synchronize with the athlete, aiding in jet-lag management and optimizing performance.

Epidemiology of sleep patterns and circadian typology in uruguayan children: The contribution of school shifts.

Healthy sleep is defined by the combination of adequate duration, good quality, and regular timing. In children, sleep thus depends on the interplay of individual, parental, organizational, community, and social variables, but only a few studies have addressed this issue in a comprehensive way nationwide. Using the Uruguayan nationally representative survey (Nutrition, Child Development, and Health Survey, Encuesta de Nutrición, Desarrollo Infantil y Salud, ENDIS), we present the first epidemiological characterization of chronobiological and sleep parameters in Latin American children. On average, Uruguayan urban children (n = 2437; 5-10-years old) showed quite late chronotypes (MSFsc = 03:53 ± 1:07), moderate misalignment (SJL = 1.0 ± 0.9 h), and adequate sleep duration (SDweek = 9.9 ± 1.0 h). Further, we show the substantial influence of school shift schedules on children's circadian typology and sleep patterns. Our results show that children attending the morning school shift have a higher risk of sleep problems than afternoon-school shift ones. The chronotype and sleep were earlier in morning-school shift children than in children attending the afternoon school shift. However, morning-school shift children had stronger misalignment, shorter sleep on school days, and a higher risk of chronic sleep deficit and non-healthy circadian misalignment (even worse in late chronotypes) than afternoon-shift children. This evidence points to the need of evaluating policies to reorganize school start times to prevent the negative effects that early schooling seems to have on children's sleep health, which has been neglected so far.

Attention to Innate Circadian Rhythm and the Impact of Its Disruption on Diabetes.

Novel strategies are required to reduce the risk of developing diabetes and/or clinical outcomes and complications of diabetes. In this regard, the role of the circadian system may be a potential candidate for the prevention of diabetes. We reviewed evidence from animal, clinical, and epidemiological studies linking the circadian system to various aspects of the pathophysiology and clinical outcomes of diabetes. The circadian clock governs genetic, metabolic, hormonal, and behavioral signals in anticipation of cyclic 24-hour events through interactions between a "central clock" in the suprachiasmatic nucleus and "peripheral clocks" in the whole body. Currently, circadian rhythmicity in humans can be subjectively or objectively assessed by measuring melatonin and glucocorticoid levels, core body temperature, peripheral blood, oral mucosa, hair follicles, rest-activity cycles, sleep diaries, and circadian chronotypes. In this review, we summarized various circadian misalignments, such as altered light-dark, sleep-wake, rest-activity, fasting-feeding, shift work, evening chronotype, and social jetlag, as well as mutations in clock genes that could contribute to the development of diabetes and poor glycemic status in patients with diabetes. Targeting critical components of the circadian system could deliver potential candidates for the treatment and prevention of type 2 diabetes mellitus in the future.

The Negative Effects of Travel on Student Athletes Through Sleep and Circadian Disruption.

Collegiate athletes must satisfy the academic obligations common to all undergraduates, but they have the additional structural and social stressors of extensive practice time, competition schedules, and frequent travel away from their home campus. Clearly such stressors can have negative impacts on both their academic and athletic performances as well as on their health. These concerns are made more acute by recent proposals and decisions to reorganize major collegiate athletic conferences. These rearrangements will require more multi-day travel that interferes with the academic work and personal schedules of athletes. Of particular concern is additional east-west travel that results in circadian rhythm disruptions commonly called jet lag that contribute to the loss of amount as well as quality of sleep. Circadian misalignment and sleep deprivation and/or sleep disturbances have profound effects on physical and mental health and performance. We, as concerned scientists and physicians with relevant expertise, developed this white paper to raise awareness of these challenges to the wellbeing of our student-athletes and their co-travelers. We also offer practical steps to mitigate the negative consequences of collegiate travel schedules. We discuss the importance of bedtime protocols, the availability of early afternoon naps, and adherence to scheduled lighting exposure protocols before, during, and after travel, with support from wearables and apps. We call upon departments of athletics to engage with sleep and circadian experts to advise and help design tailored implementation of these mitigating practices that could contribute to the current and long-term health and wellbeing of their students and their staff members.

Disruption of circadian rhythms promotes alcohol use: a systematic review.

This systematic review investigates the bidirectional relationship between alcohol consumption and disrupted circadian rhythms. The goal of this study was to identify (i) the types of circadian rhythm disruptors (i.e. social jet lag, extreme chronotypes, and night shift work) associated with altered alcohol use and (ii) whether sex differences in the consequences of circadian disruption exist. We conducted a search of PubMed, Embase, and PsycINFO exclusively on human research. We identified 177 articles that met the inclusion criteria. Our analyses revealed that social jet lag and the extreme chronotype referred to as eveningness were consistently associated with increased alcohol consumption. Relationships between night shift work and alcohol consumption were variable; half of articles reported no effect of night shift work on alcohol consumption. Both sexes were included as participants in the majority of the chronotype and social jet lag papers, with no sex difference apparent in alcohol consumption. The night shift research, however, contained fewer studies that included both sexes. Not all forms of circadian disruption are associated with comparable patterns of alcohol use. The most at-risk individuals for increased alcohol consumption are those with social jet lag or those of an eveningness chronotype. Direct testing of the associations in this review should be conducted to evaluate the relationships among circadian disruption, alcohol intake, and sex differences to provide insight into temporal risk factors associated with development of alcohol use disorder.

Melatonin Does Not Affect the Stress-Induced Phase Shifts of Peripheral Clocks in Male Mice.

Repeated or chronic stress can change the phase of peripheral circadian rhythms. Melatonin (Mel) is thought to be a circadian clock-controlled signal that might play a role in synchronizing peripheral rhythms, in addition to its direct suppressing effects on the stress axis. In this study we test whether Mel can reduce the social-defeat stress-induced phase shifts in peripheral rhythms, either by modulating circadian phase or by modulating the stress axis. Two experiments were performed with male Mel-deficient C57BL/6J mice carrying the circadian reporter gene construct (PER2::LUC). In the first experiment, mice received night-restricted (ZT11-21) Mel in their drinking water, resulting in physiological levels of plasma Mel peaking in the early dark phase. This treatment facilitated re-entrainment of the activity rhythm to a shifted light-dark cycle, but did not prevent the stress-induced (ZT21-22) reduction of activity during stress days. Also, this treatment did not attenuate the phase-delaying effects of stress in peripheral clocks in the pituitary, lung, and kidney. In a second experiment, pituitary, lung, and kidney collected from naive mice (ZT22-23), were treated with Mel, dexamethasone (Dex), or a combination of the two. Dex application affected PER2 rhythms in the pituitary, kidney, and lung by changing period, phase, or both. Administering Mel did not influence PER2 rhythms nor did it alleviate Dex-induced delays in PER2 rhythms in those tissues. We conclude that exogenous Mel is insufficient to affect peripheral PER2 rhythms and reduce stress effects on locomotor activity and phase changes in peripheral tissues.